This invention relates to an apparatus for measuring quantities of fiber forming a fiber lap to be introduced into a textile machine. The apparatus may be of the type which, at several locations along the width of the fiber lap, mechanically detects thickness deviations and, with the intermediary of a transducer, applies the sensed signals to an evaluating computer which includes a display device.
According to a known apparatus of the above type, feeler sensors (pivoted "pedals") which contact one face of the fiber lap, are used directly for detecting the lap thickness. This arrangement is operated under the assumption that the thickness fluctuations correspond to weight fluctuations, that is, only analog values related to weight are obtained. In case of a uniform fiber consistency and otherwise identical production parameters such an arrangement is satisfactory if, for example, the purpose is only a comparison between two tuft feeders rather than an intention to determine absolute weights. In the known apparatus, immediately downstream of the discharge rollers which withdraw the fiber lap from the bottom of the feed chute of the tuft feeder, there is installed a transfer tray which guides the fiber lap to a measuring roller against which the fiber material is pressed by the pedal faces which have a width of, for example, 100 mm. In case of thickness fluctuations in the fiber lap, the pedals-- which are uniformly distributed along the width of the fiber lap-- undergo corresponding excursions and thus detect the lap thickness. The motions of the pedals are transformed into electric signals by path sensors, for example, plunger coil-plunger anchor units. The electric signals are continuously applied to an evaluating computer. Further, the roller speed is also detected and applied to the computer. For each pedal, the time is calculated which is required for the passage of, for example, a 100 mm length of the fiber lap. The thickness values associated with the time period are integrated over the calculated time. In this manner, there is obtained a mean thickness of a control surface of 100 mm width (that is, the width of the pedal face contacting the fiber lap) and 1 mm length (corresponding to the measuring number). After a measuring path of 100 mm is travelled, a pause follows which is of such a length that in the running direction a distance to the subsequent measured surface is obtained whose magnitude equals the distance between the measured surfaces viewed along the lap width. The measurements are performed in sequence in the running direction at the corresponding distances and, subsequently, the total evaluation takes place. The determined thickness values may be converted into fiber lap weight. This requires a weighing of the entire quadratic surface. For a calibration, such a weight may be brought into relationship with the mean value of all thickness values. It is a disadvantage of this arrangement that the calibration process has to be repeated for each fiber material and each time the production parameters are changed.